JPH03290316A - Production of bi-based oxide superconductor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is expected to be used as a superconducting magnet wire for magnetic resonance imaging systems (MRI-CT), etc., and as a conductive material for superconducting power transmission, etc. The present invention relates to a method for producing a Bi-based high critical temperature oxide superconducting material, which is currently under development research.

(Prior art) Recently, the critical temperature T at which the normal conductive state transitions to the superconducting state
Y (yttrium) whose value exceeds the liquid nitrogen temperature
Oxide superconductors such as Bi, Bi (bismuth), and Tg (thallium) have been discovered. In Bi-based oxide superconductors, the phase with the composition Bi2Sr2CaCu20x has a Tc of about 80 and Bi2Sr2Ca2C
It is known that a phase with the composition u30y has a Te of about 105. These phases with different T,
It is usually produced in a mixed state, but recently some of Bi has been added to pb.
It is known that when substituted with , a phase with a high To of 105 is likely to be generated. These oxide superconductors can be used under much more advantageous cooling conditions than conventional metallic superconductors such as Nb-Ti and Nb3Sn, which require cooling with liquid helium. Research and development is progressing as a promising superconducting material. In particular, 81-group oxide superconductors are attracting attention because they can obtain T of 100 or more without containing highly toxic elements such as T11.

However, oxide superconductors have extremely fragile mechanical properties. For this reason, the following method is used as an example of a method for processing this into a wire rod shape.

That is, after calcining a plurality of raw material powders containing elements constituting an oxide superconductor and removing unnecessary components, the calcined powder is filled into a metal tube such as Ag, and then swaged.
It is processed into a wire of a desired diameter or a tape of a desired thickness by methods such as drawing or rolling, and then heat-treated to cause a solid phase reaction in the compressed mixed powder inside the metal tube to form an oxidized product with a desired composition. We generate physical superconductors and manufacture superconducting wires.

However, in the conventional manufacturing method of Bi-based oxide superconductors, it is difficult to mix the raw material powder completely uniformly.
Even when heat treatment is performed at a relatively high temperature, there is a problem that the entire superconductor does not have a completely uniform composition. In addition, because there are many fine holes inside the superconductor, it lacks density.
There was a problem in that it was difficult to increase the critical current density J, which is important for practical use. Furthermore, in oxide superconductors, grain boundaries often impede transport current. For this reason, it is important to make the crystal grains as large as possible and reduce the number of grain boundaries.
It is necessary to obtain Furthermore, the superconducting properties of a Bi-based oxide superconductor differ significantly in both the C-axis direction and the AB-plane direction of its crystal. For this reason, it is necessary to align the orientation of each crystal and apply a magnetic field or flow an electric current in the direction with the best characteristics.

The inventors have developed a Bi-based oxide superconductor as the first low-melting phase.
divided into an oxide element and a second oxide element in a high melting point phase,
Bi-based oxide superconductor was fabricated by diffusion method (1
Spring 988 Low Temperature Engineering and Superconductivity Society Proceedings, 126 pages). According to this diffusion method, a dense superconducting phase with a uniform composition can be generated and excellent superconducting properties can be obtained.

(Problems to be Solved by the Invention) The present invention provides a solution to the melting point of the first oxide element, which is a low melting point phase constituting the composite, by replacing a part of Bi with Ll in a Bi-based oxide superconductor. By further lowering the temperature and promoting the diffusion of this and the second oxide element, which is a high melting point phase, the Bi-based oxide superconductor produced by the above-mentioned diffusion method, which was previously developed by the present inventors, can be produced at a lower temperature and in a shorter time. A dense acetyl oxide superconductor having a uniform composition is produced by heat treatment for several hours. As a result, the critical temperature T of the 81-group oxide superconductor obtained. This improves the critical current density Jc without reducing the current density Jc.

(Means for Solving the Problems) The present invention provides a method for manufacturing a Bi-based oxide superconductor, which includes:
Part of Bi is replaced with Li as the first oxide element,
Bi-L 1-Cu-0, Bi-L 1-Ca-Cu
-0, etc., and as the second oxide element, SrCaOsSr-Ca-Cu-0
An oxide composed of etc. is used. Next, a composite obtained by mixing oxide powders of the first oxide element and the second oxide element, or a substrate made of the second oxide element, is coated with the first oxide element. A composite is prepared by coating the powder and then subjected to a diffusion heat treatment.

The Bi-based oxide superconductor produced in the present invention includes the aforementioned Bi-Li-8r-Ca-Cu-Os and one in which a part of Bi is replaced with pb.

The first oxide element desirably has a melting point as low as possible in order to promote diffusion during heat treatment of the composite. This first oxide element is Bi20*, Li2C
O3, CuO1 Add as necessary CaCO3, Pb3O
It is produced by mixing raw material powders such as No. 4 in a predetermined composition ratio and performing calcination or the like.

The second oxide element also functions as a base for diffusing the composite, and preferably has a melting point as high as possible. This second oxide element is S rcOi , Ca
Mixing raw material powders such as C0, CuO, etc. in a predetermined composition ratio,
It is manufactured through a process such as calcination. As a result of research conducted by the inventors using thermal analysis methods, etc., it has been found that Bi-based oxides that do not contain Sr are suitable as the first oxide element, while Bi-based oxides that do not contain Sr are suitable for the second oxide element. This was obtained by discovering that a Sr-based oxide containing no Bi is suitable. Here, the first oxide element having the above structure had a melting point of about 550°C to 750°C, and by adding Li, the melting point could be lowered by about 100°C. Further, the second oxide element having the above structure had a melting point of 1000° C. or higher.

In the case of the Bi-Li-Cu-0 system of the first oxide element, the composition ratio (atomic ratio) is Li 0.05 with respect to Bil.
~0.5, Ca0-1.5, Cu0.5-2.
It is preferably in the range of 0. Sr- of the second oxide element
In the case of Ca-Cu-0 system, the composition ratio (atomic ratio) is Srl
For, Ca 0.5-1.5, Cu 0.5
It is desirable that it be in the range of ~2.0. Here, the first
Since the oxide element and the second oxide element take the form of an oxide, the content of 0 is theoretically calculated from the amount of the other element. In the present invention, if the composition ratio deviates from these ranges, it becomes difficult to obtain good superconducting properties. Note that in the first oxide element, Bi may be replaced with PB at a composition ratio (atomic ratio) o in the range of 1 to 0.5.

As a specific example of applying the present invention to the production of a wire rod, a composite obtained by filling a base sheath with a mixed powder of a first oxide element and a second oxide element is subjected to wire drawing, flat roll rolling, etc. There is also a method of repeating heat treatment to produce tapes, wires, etc. Alternatively, after the second oxide element is continuously applied onto a mechanically strong tape or linear base material by a method such as a spray method or a printing method, A composite tape or wire is produced by carrying out a heat treatment and then sequentially coating its surface with a first oxide element in a similar manner. Next, a diffusion heat treatment is performed. This diffusion heat treatment can provide a material with better performance if the primary diffusion heat treatment is performed at a low temperature and then the secondary diffusion heat treatment is performed at a high temperature.

The primary diffusion heat treatment temperature is in the range of 550°C to 750°C, and the secondary diffusion heat treatment temperature is in the range of 750°C to 900°C. The second diffusion heat treatment temperature is near the melting point of the first oxide element, and the diffusion reaction can bring the first oxide element and the second oxide element into close contact with each other and eliminate pores.

The secondary diffusion heat treatment temperature is near the formation temperature of the Bi-based oxide superconductor, forming a crystal structure with a high T.

Furthermore, even if the -order diffusion heat treatment is omitted, it is possible to generate a superconducting phase, or the component system of the first oxide element may rapidly penetrate and swell, causing cracks.

Therefore, when omitting the secondary diffusion heat treatment, the temperature increase during the secondary diffusion heat treatment should be increased by 1°C/1°C in the temperature range of 600°C or higher.
Must be done later than 1 minute. Also, -order diffusion heat treatment or 5
At temperatures below 50°C, there is no effect, and secondary diffusion heat treatment
A temperature of 00° C. or higher is not preferable because the second phase or the like is precipitated by diffusion or melting.

Thus, according to the invention, by subjecting the composite to a diffusion heat treatment, the components of the first oxide element diffuse into and react with the second oxide element. A uniform, dense, high-T, superconducting phase is generated on the surface of the material.

[Effect of the invention] As explained above, Bi diffusion method based on the present invention
In the method for producing base oxide superconductors, the first phase, which is a low melting point phase, is
By adding Li to the second oxide element, the melting point is lower than that of the low melting point phase used in the conventional diffusion method, and diffusion with the second oxide element is promoted during heat treatment. Short-time heat treatment becomes possible. Therefore, it becomes easier to manufacture devices using superconductors. In addition, it is possible to produce i-acetyl oxide superconductors that are dense, free of pores, and have a uniform composition.Additionally, the addition of Li promotes diffusion, causing the crystal grains of the superconducting phase to grow larger and reducing grain boundaries, resulting in superconducting properties. It is possible to improve J without reducing Tc. Furthermore, unlike the usual powder sintering method, a Bi-based oxide superconductor with excellent crystal orientation can also be produced by applying a diffusion method.

Example I B 1203, L i2 CO3, Ca CO3, C
U O raw material powder (B 1o9L lo, + )2
It was blended to have a composition of CaCu0X, calcined at 650°C for 6 hours to remove unnecessary components such as 002, and crushed.
After calcining again at 670° C. for 8 hours, it was pulverized to produce a first oxide element. On the other hand, SrCO3, CaC0,
, Cu0 (7) raw material powder was blended to have a composition of Sr2 (: aCu205, calcined at 900 ° C. for 6 hours, then crushed, calcined again at 1000 ° C. for 12 hours, and then crushed, A second oxide element was produced.Equimolar amounts of the produced first oxide element and second oxide element were mixed, and (Bio,Lio,+)2Sr2
After adjusting the composition to have a composition of Ca2Cu30Y, this mixed powder was pressed under a load of 2.7 t/cd and molded into a rectangular shape with a width of 5 mm, a length of 22 mm, and a thickness of 1 mm to produce a composite. This composite was subjected to diffusion heat treatment at 820°C for 20 hours, and then pressed (2.7 t/h) to orient the crystal grains.
CD) was inserted in between and heated again at 820"C for 20 hours.
Sample 1 was prepared by performing diffusion heat treatment.

In addition, as a comparative example, Bi2Sr2Ca2 which does not contain Li
Sample 2 having a composition of Cu30y was produced in the same manner as above. However, if Li is not included, the diffusion heat treatment is 8
The temperature was 50°C. Table 1 shows the TeCoff 5et) and Jc at 4.2K of these samples measured by the DC 4-terminal method. Sample 1 has almost the same Te as Comparative Example Sample 2, but J has increased about twice.

Example 2 Raw material powder of SrCO9CaC0, CuO was converted into Sr2Ca
Blended to have a composition of 2cu2o6, calcined at 900℃ for 6 hours to remove unnecessary components such as Co2, and crushed.
After calcining again at 1000°C for 12 hours, it was pulverized.

This powder was pressed with a load of 2.5t/cd to a width of 5 m.
m, formed into a rectangular shape with a length of 22 mm and a thickness of 1 mm.
A second oxide element serving as a base was produced by firing at 00''C for 18 hours.

On the other hand, the raw material powders of Bi2O3, Li2co3, and cuo (
B io, s L io, z ) 2 CuO An oxide element of No. 1 was prepared. Next, the powder of the component forming the first oxide element is suspended in ethyl alcohol, and about 0.1 g of the slurry is applied onto the second oxide element as a base to form a composite. was created. This composite was subjected to secondary diffusion heat treatment at 675°C for 10 hours and then secondary diffusion heat treatment at 800'C for 40 hours to prepare Sample 3. Note that all the heat treatments in this example were performed in the atmosphere and slowly cooled to room temperature. In addition, as a comparative example, element 2 is Sr2Ca2Cu20 for a sample that does not contain Li.
b The first oxide element was made into a composite using Bi2Cu0X in the same manner as above, and then subjected to -order diffusion heat treatment at 700°C.
Sample 4 was prepared by performing secondary diffusion heat treatment at 850° C. for 40 hours. T, (ofT 5et) of these samples measured by DC 4-terminal method and J at 4.2K.
, are shown in Table 1.

Although sample 3 has a lower diffusion heat treatment temperature than sample 4 of the comparative example, T1 is almost the same and 31 is an improved value.

Example 3 Bi203, Li2CO3, Pb304, Ca
Raw material powders of CO3 and CuO (B L o, s L i
.

Pbol) CaCu0X composition, 6
The product was calcined at 20° C. for 6 hours to remove unnecessary components such as CO2, pulverized, calcined again at 620° C. for 8 hours, and then pulverized to produce a first oxide element. On the other hand, S rco
, , CaC0m , CuO raw material powder is Srz Ca
The composition was blended to have a composition of CL1205, calcined at 900°C for 6 hours, crushed, calcined again at 1000°C for 12 hours, and then crushed to produce a second oxide element.

The prepared first oxide element and second oxide element are weighed and mixed in equimolar amounts (Bio, 8Li).

Pbo,+)2Sr2Ca2Cu30y, the mixed powder was pressed with a load of 2.7t/c- to form a strip shape with a width of 5 mm, a length of 22 mm, and a thickness of 11 mm to form a composite. Created. This complex was heated at 760℃
After performing diffusion heat treatment for 20 hours at
Sample 5 was prepared by performing diffusion heat treatment at 60° C. for 20 hours. In addition, as a comparative example, Li is not included (B io, s
Sample 6 having a composition of Pbo2)2Sr2Ca2(:u30Y) was prepared in the same manner as above, with the diffusion heat treatment temperature set at 845°C.The T c (off' 5et ) and 77K
J in is shown in Table 1. Sample 5 has substantially the same Te and an improved value of J, even though the diffusion heat treatment temperature is lower, as in Example 2, compared to Sample 6 of the comparative example.

Table 1 Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 T in each sample and Jc Tc (K) 4 (Comparative example) 72 1 (Comparative example) 74 04 (Comparative example) 103 The value of the Jc (A/cI#) 3200 (4,2K) 1700 (4,2K) 6000 (4,2K) 4100 (4,2K) 12.00 (77K) 700 (77K)

Claims (6)

[Claims] (1) By a diffusion reaction between a first oxide element composed of at least the elements Bi-Li-Cu-O and a second oxide element composed of at least the elements Sr-Ca-O. A method for producing a Bi-based oxide superconductor, the method comprising: producing a Bi-based oxide superconductor. (2) The first oxide element is Bi-Li-Ca-C
Composed of u-O elements, the atomic ratio of which is Bi: 1, Li0.05-0.5, Ca0-1.5, Cu0.5
~2.0, and the second oxide element is Sr
It is composed of the elements -Ca-Cu-O, and its atomic ratio is S
Ca0.5-1.5, Cu0.5-2.0, where r is 1
2. The method for producing a Bi-based oxide superconductor according to claim 1, wherein the Bi-based oxide superconductor is in the following range. (3) The Bi-based oxide according to claim 1 or 2, wherein a composite obtained by mixing powders of the first oxide element and the second oxide element is subjected to a diffusion heat treatment. Method for manufacturing superconductors. (4) Bi-based oxidation according to claim 1 or 2, characterized in that the composite obtained by coating the first oxide element on the substrate made of the second oxide element is subjected to a diffusion heat treatment. Method for manufacturing physical superconductors. (5) Part of the Bi of the first oxide element to Bi1,
Bi according to any one of claims 1 to 4, characterized in that Bi is substituted with Pb at a composition ratio of 0.1 to 0.5 atomic %.
Method for producing base oxide superconductor. (6) The heat treatment includes primary diffusion heat treatment in the range of 550°C to 750°C, and 750°C performed after this heat treatment.
The method for producing a Bi-based oxide superconductor according to any one of claims 1 to 5, comprising a secondary diffusion heat treatment at a temperature in the range of -900C.